com.saxonica.expr

## Class IndexedValue<T extends Item>

- java.lang.Object
- - com.saxonica.expr.IndexedValue<T>

- All Implemented Interfaces:
    GroundedValue, Sequence

      public class IndexedValue<T extends Item>
      extends Object
      implements GroundedValue

  A representation of a (sequence) value that allows the construction of one or more indexes to provide rapid access to the items in the sequence.

- - ### Constructor Summary

    Constructors
    Constructor and Description
    `IndexedValue(SequenceIterator<? extends T> iter)` Construct an indexed value (that is, a value that is capable of being indexed).

  - ### Method Summary

    Methods
    Modifier and Type | Method and Description
    --- | ---
    `boolean` | `effectiveBooleanValue()` Get the effective boolean value of this sequence
    `SequenceIterator<T>` | `findItems(Expression use, SequenceIterator values, boolean convertUntypedToOther, boolean firstOnly, AtomicComparer comparer, XPathContext context)` Retrieve items that match a given index value
    `int` | `getLength()` Get the length of the sequence
    `String` | `getStringValue()` Get the string value of this sequence.
    `CharSequence` | `getStringValueCS()` Get the string value of this sequence.
    `Item` | `head()` Get the first item in the sequence.
    `T` | `itemAt(int n)` Get the n'th item in the sequence (starting from 0).
    `SequenceIterator<T>` | `iterate()` Return an Iterator to iterate over the values of a sequence.
    `GroundedValue` | `reduce()` Reduce the sequence to its simplest form.
    `GroundedValue` | `subsequence(int start, int length)` Get a subsequence of the value

    - ### Methods inherited from class java.lang.Object

      `clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait`

- - ### Constructor Detail

    - #### IndexedValue

          public IndexedValue(SequenceIterator<? extends T> iter)
                       throws XPathException

      Construct an indexed value (that is, a value that is capable of being indexed). Initially there will be no indexes, these are added later.
      Parameters:
        `iter` - iterator over the items to be included in the indexed value
      Throws:
        `XPathException` - if an error occurs reading the iterator

  - ### Method Detail

    - #### iterate

          public SequenceIterator<T> iterate()
                                                   throws XPathException

      Return an Iterator to iterate over the values of a sequence. The value of every expression can be regarded as a sequence, so this method is supported for all expressions. This default implementation handles iteration for expressions that return singleton values: for non-singleton expressions, the subclass must provide its own implementation.
      Specified by:
        `iterate` in interface `Sequence`
      Returns:
        a SequenceIterator that can be used to iterate over the result of the expression
      Throws:
        `XPathException` - if any dynamic error occurs evaluating the expression

    - #### itemAt

          public T itemAt(int n)

      Get the n'th item in the sequence (starting from 0). This is defined for all Values, but its real benefits come for a sequence Value stored extensionally (or for a MemoClosure, once all the values have been read)
      Specified by:
        `itemAt` in interface `GroundedValue`
      Parameters:
        `n` - position of the required item, counting from zero.
      Returns:
        the n'th item in the sequence, where the first item in the sequence is numbered zero. If n is negative or >= the length of the sequence, returns null.

    - #### getLength

          public int getLength()

      Get the length of the sequence
      Specified by:
        `getLength` in interface `GroundedValue`
      Returns:
        the number of items in the sequence

    - #### findItems

          public SequenceIterator<T> findItems(Expression use,
                                      SequenceIterator values,
                                      boolean convertUntypedToOther,
                                      boolean firstOnly,
                                      AtomicComparer comparer,
                                      XPathContext context)
                                                     throws XPathException

      Retrieve items that match a given index value
      Parameters:
        `use` - the expression whose value is to be matched
        `values` - the set of values to be found
        `convertUntypedToOther` - true if untypedAtomic values are to be converted to the type of the other operand
        `firstOnly` - true if only the first matching item is required
        `comparer` - AtomicComparer used to compare values for equality (encapsulates a collation if necessary)
        `context` - the dynamic evaluation context @return an iterator over the items that match the specified values
      Throws:
        `XPathException`

    - #### subsequence

          public GroundedValue subsequence(int start,
                                  int length)

      Get a subsequence of the value
      Specified by:
        `subsequence` in interface `GroundedValue`
      Parameters:
        `start` - the index of the first item to be included in the result, counting from zero. A negative value is taken as zero. If the value is beyond the end of the sequence, an empty sequence is returned
        `length` - the number of items to be included in the result. Specify Integer.MAX_VALUE to get the subsequence up to the end of the base sequence. If the value is negative, an empty sequence is returned. If the value goes off the end of the sequence, the result returns items up to the end of the sequence
      Returns:
        the required subsequence. If min is

    - #### effectiveBooleanValue

          public boolean effectiveBooleanValue()
                                        throws XPathException

      Description copied from interface: `GroundedValue`
      Get the effective boolean value of this sequence
      Specified by:
        `effectiveBooleanValue` in interface `GroundedValue`
      Returns:
        the effective boolean value
      Throws:
        `XPathException` - if the sequence has no effective boolean value (for example a sequence of two integers)

    - #### getStringValue

          public String getStringValue()
                                throws XPathException

      Description copied from interface: `GroundedValue`
      Get the string value of this sequence. The string value of an item is the result of applying the string() function. The string value of a sequence is the space-separated result of applying the string-join() function using a single space as the separator
      Specified by:
        `getStringValue` in interface `GroundedValue`
      Returns:
        the string value of the sequence.
      Throws:
        `XPathException` - if the sequence contains items that have no string value (for example, function items)

    - #### getStringValueCS

          public CharSequence getStringValueCS()
                                        throws XPathException

      Description copied from interface: `GroundedValue`
      Get the string value of this sequence. The string value of an item is the result of applying the string() function. The string value of a sequence is the space-separated result of applying the string-join() function using a single space as the separator
      Specified by:
        `getStringValueCS` in interface `GroundedValue`
      Returns:
        the string value of the sequence.
      Throws:
        `XPathException` - if the sequence contains items that have no string value (for example, function items)

    - #### head

          public Item head()
                    throws XPathException

      Get the first item in the sequence.
      Specified by:
        `head` in interface `Sequence`
      Returns:
        the first item in the sequence if there is one, or null if the sequence is empty
      Throws:
        `XPathException` - in the situation where the sequence is evaluated lazily, and evaluation of the first item causes a dynamic error.

    - #### reduce

          public GroundedValue reduce()

      Reduce the sequence to its simplest form. If the value is an empty sequence, the result will be EmptySequence.getInstance(). If the value is a single atomic value, the result will be an instance of AtomicValue. If the value is a single item of any other kind, the result will be an instance of SingletonItem. Otherwise, the result will typically be unchanged.
      Specified by:
        `reduce` in interface `GroundedValue`
      Returns:
        the simplified sequence

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